Global warming and other global environmental problems as well as an energy problem that energy resources, such as oil that have been misunderstood to be unlimited, are starting to run out, are recently becoming a global common awareness.
Under such a circumstance, wind power generation, which is free from CO2 emission, is in the limelight as energy generating means that solves both the environmental problems and the energy problem. However, wind power generators can convert merely about 40% of kinetic energy of wind flowing inside the wind turbine into electric power, even with large-sized wind turbines which are regarded as being highly-efficient. If an amount of conversion is improved, the wind power generation will be in a more dominant position in relation to the environmental problems and the energy problem.
In the meantime, the output of the wind power generation is proportional to a cube of a wind velocity. Therefore, when installing a wind turbine, a windy area is selected as a site. Further, efforts have been made to collect wind to increase velocity as much as possible so as to increase power generation. Accordingly, attention has been paid to an improvement in a wind collecting element on an intake side of a wind power generator, an impeller, a diffuser, and the like, and measures have been taken to improve energy conversion efficiency as much as possible. However, these considerations and measures are all an extension of conventional turbo machine. As a matter of course, there has been a limit.
In view thereof, the inventors and other researchers have challenged such common sense in the wind power generators (see Patent Document 1). Specifically, they reached a viewpoint that it is not necessary to be bound by a streamline shape and a steady-flow way of thinking, as long as an objective of high output power generation can be achieved. Conventional fluid machines are based on a streamline shape and a steady-flow that are easy to analyze, and it is not an exaggeration to say that there are no turbo machines that utilize a non-streamline shape (a bluff body) and an unsteady flow. However, even with a non-streamline shape and an unsteady flow, the original objective is fulfilled if it possible to realize a steady-flow and to increase flow velocity of an internal flow than the conventional flow so that the flow is improved. The “streamline shape” and the “non-streamline shape” are defined hereinbelow. The streamline shape is a shape according to which a flow streams without substantially separating from an object surface within a range of Reynolds numbers Re used in fluid machines, while the non-streamline shape is a shape other than that according to which the separation occurs.
In order to achieve this, the inventors et al. have proposed a wind power generator of Patent Document 1. This wind power generator has a cylindrical wind tunnel body and a power-generating wind turbine disposed in near a wind inlet of the wind tunnel body. The wind power generator has a structure in which a flat flange perpendicular to a flow direction of wind is arranged on an outer side of an edge of an outlet of the wind tunnel body to cause a wind flowing outside the wind tunnel body to collide therewith so as to form intensive vortices on the back side, and in which an inclination angle of a side body portion with respect to an axis of the wind tunnel body is within a range of 5° to 25°. The flange has a width that is 10% to 100% of the minimum inner diameter of the wind tunnel body.
Forming vortices against the flow by placing such a flange (a ring) is beyond common sense in the conventional fluid machines. The vortices formed behind the flange are vortex formation which may be referred to as so called Kerman vortices that are generated alternately at inner and outer circumferences on a downstream side of a concentric ring. The vortices are alternately (in an unsteady manner) generated at certain timings, and the vortices reduce the pressure in the vicinity of the outlet of the wind tunnel body, whereby the flow velocity of the internal flow is improved due to pressure difference.
The structure of this wind power generator, in other words, created a new category (a type of fluid machine having a non-streamline shape) in the wind power generators or in the fluid machines. The structure controls the entire flow around the fluid machine by means of the vortices generated on the outlet side, to take stronger wind into the interior of the machine, and to efficiently speed up the fluid by causing the fluid to smoothly flow along an inner wall surface toward the outlet without separation from the inner wall surface. This speeded-up flow enables power generation with higher output than before.    Patent Document 1: JP 3621975 B2